Give it up!
Here at SG we mostly focus on acquisitions - what you can buy to make your life a little better, a little more chic. But just as important it what you can get rid of to improve your life and your style. Everyone has too much stuff, it's a universal problem, but it's one that can be addressed. Here are some tips on cleaning out stuff you don't need.
For clothes, clean out your closet using the "box method" detailed at StylePhyle. Give your "charity" clothes to Goodwill, the Salvation Army, or Vietnam Veterans of America, who in some areas will come to pick up your donations.
For knick-knacks, remember that just because it was a gift doesn't mean you have to keep it. Wedding favors are not particularly meaningful gifts, so that salt and pepper shaker pair can go, as can the porcelain flower. That really ugly platter your aunt gave you for Christmas six years ago shouldn't stick around either. If items do have real meaning to you, decide how to display them to their best advantage, or pack them carefully away until you have the space to do so.
Take a good look at your furniture and see if any of your old pieces need to go. Leftovers from college dorm roms often fall into this category. If you are keeping furniture, keep it because you like it and you use it. If it doesn't fit both categories, you shouldn't keep it around, unless it's a family heirloom you just don't have space for yet. Sell or give away your furniture on Craigslist.
And books. I have a lot of books, and I find it very hard to part with them. But if you haven't read a book in years, and have no plans to read it again, it should go. Donate used books to your local library, and sell your old textbooks or give them to a local high school.
Old sports equipment, old computers, and mismatched dishes kitchenware should also be dealt with ruthlessly.